This invention lies in the field of video apparatus. More particularly, it concerns apparatus for use with a Charge Coupled Device video camera which has at least one blemish in its photosensitive surface.
The recent development of a Charge Coupled Device (CDD) camera having standard television resolution capability has led to use in applications formerly filed by orthocon or vidicon tubes. The CCD camera is basically a sampled-data system using discreet silicon cells to sample a video scene. Due to the high density of cells on the chip and limitations on the state of the art for fabricating chips, a certain minimum amount of cells will be defective. A defective cell appears as a saturated video point when displayed on a television monitor. For many uses the saturated video point must be removed.
A similar problem can arise in prior art camera systems when there is a flaw in the photosensitive surface. In addition, camera tubes produce a form of distortion called shading distortion which is not present in CCD cameras. Prior approaches often combined shading and spot distortion correction as in U.S. Pat. No. 2,445,040. Shading distortion is conventionally corrected by a series of oscillators which produce signal to cancel tube distortion as in U.S. Pat. No. 2,658,104. As a CCD camera has no shading distortion such circuits fulfill no purpose as they do not correct for defective cells.
Prior art blemish correction as applied to tube cameras required a pre-programming of the location of the defective spot as in U.S. Pat. No. 3,864,567. Alternatively, a mask can be used for this purpose as in U.S. Pat. No. 2,445,040. Systems that automatically correct for flaws have not been developed because the shading distortion of tube circuits would activate the blemish correction circuit and distort the picture.
Heretofore there has been shown no way for automatically correcting for a defective cell on a CCD camera.